In the conventional direct communication system, a user equipment (UE) which desires to perform direct communication must firstly transmit a resource synchronization request to the base station. After receiving the resource synchronization request from the UE, the base station allocates an available network resource to the UE so that the direct communication is subsequently performed by the UE.
To synchronize the UE having small communication coverage with a base station, a lot of base stations may be deployed to extend the network coverage so as to receive the resource synchronization request from the UE, or alternatively, the synchronization may be accomplished by using a relay node.
However, the aforesaid solutions might lead to a significant increase of the hardware cost, and synchronization signals for resource synchronization that are transmitted by different relay nodes might cause wastes in the network resources. Moreover, in case the UE is to perform the synchronization via different relay nodes, it is impossible for the UE to accurately achieve resource synchronization mainly with a single source because the UE cannot know synchronization sources of different relay nodes.
Accordingly, efforts still have to be made in the art to overcome the shortcomings of the conventional direct communication network so as to accomplish resource synchronization communications at a low hardware deployment cost, with a high network resource utilization factor and at a high resource synchronization accuracy rate.